This invention relates generally to gas chromatography, and more particularly, is directed to the automation of sample injections in a gas chromatograph.
Nitroglycerin assays are performed by gas chromatographic analysis of nitroglycerin in plasma, using electron capture detection. Originally, such nitroglycerin analyses were carried out using packed column gas chromatography. Recently, however, state of the art capillary gas chromatography has been used for such analyses.
When performing such nitroglycerin assays with state of the art gas chromatographs, it is generally required that the gas chromatograph provide a sensitivity which permits detection of the nitroglycerin to a level of 25 picograms/milliliter (pg/ml) of plasma. It has been found that the VISTA 6000 model gas chromatograph sold by Varian Associates, Inc., 611 Hansen Way, Palo Alto, Calif. 94303, gives excellent sensitivity and meets this requirement.
Varian presently sells an autosampler for use with its gas chromatograph. The autosampler mounts on the gas chromatograph and provides automatic, multiple sample injections to an injection port of the gas chromatograph. However, the Varian autosampler requires at least 50 microliters (.mu.l) of sample for one injection. In certain circumstances, however, such as the aforementioned nitroglycerin assays, it may be required that the autosampler perform multiple injections with the same sample when only 50 .mu.l or less of sample volume is available. This means that samples must be prepared again.
Therefore, it has been necessary to manually inject the samples when performing nitroglycerin assays. As a result, hours of valuable research time have been spent peforming routine sample injections. Consequently, laboratory personnel have been required to work overtime to complete analyses, resulting in physical and mental fatigue.
Hewlett-Packard sells an autosampler (HP 7673A Automatic Sampler) which can perform multiple injections with a sample volume of less than 50 .mu.l. This is because the Hewlett-Packard autosampler does not use the entire sample during one injection. The Hewlett-Packard autosampler, however, cannot be mounted directly on the Varian VISTA 6000 gas chromatograph.